Buggy code:
public JDBCStore getStore ( ) { } public FilterListener getFilterListener ( String tag ) { } public Object newCompilationKey ( ) { } public boolean supportsDataStoreExecution ( ) { } protected ClassMetaData [ ] getIndependentExpressionCandidates ( ClassMetaData meta , boolean subclasses ) { } protected ExpressionFactory getExpressionFactory ( ClassMetaData meta ) { } protected ResultObjectProvider executeQuery ( Executor ex , ClassMetaData base , ClassMetaData [ ] metas , boolean subclasses , ExpressionFactory [ ] facts , QueryExpressions [ ] exps , Object [ ] params , Range range ) { } private BitSet [ ] populateUnion ( Union union , final ClassMapping [ ] mappings , final boolean subclasses , final ExpressionFactory [ ] facts , final QueryExpressions [ ] exps , final QueryExpressionsState [ ] states , final ExpContext ctx , final boolean lrs , final int eager , final long start , final long end ) { } private BitSet populateSelect ( Select sel , ClassMapping mapping , boolean subclasses , JDBCExpressionFactory fact , QueryExpressions exps , QueryExpressionsState state , ExpContext ctx , boolean lrs , int eager , long start , long end ) { } private ResultObjectProvider executeUnion ( Union union , ClassMapping [ ] mappings , QueryExpressions [ ] exps , QueryExpressionsState [ ] states , ExpContext ctx , BitSet [ ] paged ) { } private ResultObjectProvider executeSelect ( Select sel , ClassMapping mapping , QueryExpressions exps , QueryExpressionsState state , ExpContext ctx , BitSet paged , long start , long end ) { } private boolean createWhereSelects ( List sels , ClassMapping [ ] mappings , List selMappings , boolean subclasses , BitSet subclassBits , BitSet nextBits , ExpressionFactory [ ] facts , QueryExpressions [ ] exps , QueryExpressionsState [ ] states , ExpContext ctx , int subclassMode ) { } private ClassMapping [ ] getVerticalMappings ( ClassMapping mapping , boolean subclasses , QueryExpressions exps , int subclassMode ) { } private void addSubclasses ( ClassMapping mapping , Collection subs ) { } private static boolean hasVerticalSubclasses ( ClassMapping mapping ) { } private int calculateEagerMode ( QueryExpressions exps , long start , long end ) { } protected Number executeDelete ( Executor ex , ClassMetaData base , ClassMetaData [ ] metas , boolean subclasses , ExpressionFactory [ ] facts , QueryExpressions [ ] exps , Object [ ] params ) { } protected Number executeUpdate ( Executor ex , ClassMetaData base , ClassMetaData [ ] metas , boolean subclasses , ExpressionFactory [ ] facts , QueryExpressions [ ] exps , Object [ ] params ) { } private Number executeBulkOperation ( ClassMetaData [ ] metas , boolean subclasses , ExpressionFactory [ ] facts , QueryExpressions [ ] exps , Object [ ] params , Map updates ) { } private boolean isSingleTableMapping ( ClassMapping mapping , boolean subclasses ) { } private Table getTable ( FieldMapping [ ] fields , Table table ) { } private Table getTable ( FieldMapping fm , Table table ) { } protected Number executeUpdate ( ClassMetaData base , ClassMetaData [ ] metas , boolean subclasses , ExpressionFactory [ ] facts , QueryExpressions [ ] parsed , Object [ ] params ) { } protected String [ ] getDataStoreActions ( ClassMetaData base , ClassMetaData [ ] metas , boolean subclasses , ExpressionFactory [ ] facts , QueryExpressions [ ] exps , Object [ ] params , Range range ) { } protected int executeUpdate ( Connection conn , PreparedStatement stmnt , SQLBuffer sqlBuf , boolean isUpdate ) throws SQLException { } protected PreparedStatement prepareStatement ( Connection conn , SQLBuffer sql ) throws SQLException { } public Object evaluate ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { } private Object handleMathVal ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { } private Object handleConcatVal ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { Concat concatVal = ( ( Concat ) ( value ) ) ; Val value1 = concatVal . getVal1 ( ) ; Object val1 = getValue ( value1 , ob , params , sm ) ; Val value2 = concatVal . getVal2 ( ) ; Object val2 = getValue ( value2 , ob , params , sm ) ; <START_BUG> return new StringBuffer ( 100 ) . append ( val1 ) . append ( val2 ) . toString ( ) ; <END_BUG> } private Object handleSubstringVal ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { } private Object handleArgsVal ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { } private Object handleLowerVal ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { } private Object handleUpperVal ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { } private Object handleLengthVal ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { } private Object handleTrimVal ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { } private String trimLeading ( String value , char trimChar ) { } private String trimTrailing ( String value , char trimChar ) { } private Object handleIndexOfVal ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { } private Object handleAbsVal ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { } private Object handleSqrtVal ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { } private Object getValue ( Object value , Object ob , Object [ ] params , OpenJPAStateManager sm ) { } private Object getValue ( Object ob , FieldMapping fmd , OpenJPAStateManager sm ) { } private static class ThreadLocalContext extends ThreadLocal < Context [ ] > { public Context [ ] initialValue ( ) { } }

Fix:
return new StringBuilder ( 100 ) . append ( val1 ) . append ( val2 ) . toString ( ) ;